Petroleum samples are complicated hydrocarbon mixtures containing paraffins, cyclic paraffins, multiring aromatics, and various heteroatomic hydrocarbons (most commonly O, S, and N). Virgin petroleum crude oils contain molecules of a wide boiling point range from highly volatile C4 hydrocarbons to nonvolatile asphaltenes. Analysis of petroleum composition of various boiling ranges is valuable for improving the operation of many subsequent processes.
Determining the composition of a petroleum sample can be beneficial for a variety of reasons. For example, the composition of a distillate boiling range sample can provide insight into the energy value of the sample as well as the cold flow properties.
U.S. Pat. No. 7,598,487 describes methods for characterizing the composition of a petroleum sample, such as a distillate sample. The sample is characterized using two types of techniques. One type of characterization is to use a gas chromatograph with a field ionization time-of-flight mass spectrometer to determine the identity of species within a sample. This chromatographic characterization is used in combination with another technique that can provide relative amounts of general classes of compounds within the sample. Supercritical fluid chromatography is described as an example of a technique for determining relative amounts of the compound classes in a sample.